Drum brakes

ABSTRACT

In an internal shoe drum brake in which a pair of shoes each have one end in sliding engagement with an abutment surface fast to a back plate, and brake-actuating means carried by the back plate operate to force apart the other ends of the two shoes, a single spring serves both to return the shoes towards one another (holding them pressed against the abutment surfaces in the brakes-off condition) and also to hold down the shoes against the face of the back plate. In the construction described and illustrated, a spring of generally C form operates to urge towards one another a pair of coupling members, each of which is anchored at one end to the back plate, and extends through an aperture in the web of one of the shoes, a portion of the coupling member which is inclined to the plane of the back plate making sliding engagement with the margin of the aperture.

United States Patent [72] Inventor Antony W. Harrison 3,203,512 8/1965 Lepelletier 188/216X Birmingham, England 3,337,007 8/1967 Swift .1 l88/78(.9) 9gp;- 2 3 1969 FOREIGN PATENTS l e e Patented Jan 12 1971 1,438,924 4/1966 France 188/216 [73] Assignee Giling Limited Primary Examiner-George E. A. l-lalvosa Birmingham, England Attorney-Scrivener, Parker, Scrivener and Clarke a British Company [32] Priority Mar. 1, 1968 [33] Great Britain [31 1 10208/68 ABSTRACT: In an internal shoe drum brake in which a pair of shoes each have one end in sliding engagement with an abutment surface fast to a back plate, and brake-actuating means [54] Figs carried by the back plate operate to force apart the other ends of the two shoes, a single spring serves both to return the shoes [52] US. Cl 188/78, towards one another (holding them pressed against th b 183/216 ment surfaces in the brakes-off condition) and also to hold [51] Int. down the hoes against the face of the back plate In the con- [50] Field of Search l88/78.9, Struction d ib d d illustrated, a spring of generally C 216 form operates to urge towards one another a pair of coupling members, each of which is anchored at one end to the back [56] References C'ted plate, and extends through an aperture in the web of one of UNITED STATES PATENTS the shoes, a portion of the coupling member which is inclined 2,509,643 5/1950 House 188/78(.9) to the plane of the back plate making sliding engagement with 3,061,051 /1962 Swift- 188/78( .9) the margin of the aperture.

a a? X F I 34 4T b 5 3 H 26 J Ir Q 9 7 g 22 \l E 37 W I l L I t3 I g FIG 2 l 24 21 7 m PATENTEU JAN 112ml sum 1 n? 3 PATENTEnJAmzlsn SHEET 2 [1F 3 DRUM BRAKES This invention relates to internal shoe drum brakes.

In drum brakes in which each shoe has one end in contact with an abutment su-face on the brake back plate, or torque plate, (the brake-actuating means operating to force apart the opposite ends of the snoes) it is necessary or desirable, in order to stabilize the shoes in the brakes-off condition, that the shoes should not only be spring loaded against the abutment surfaces by the shoe return spring butshould also be held down by spring means against the face of the backplate.

In accordance with the present invention, there is provided an internal shoe drum brake including a back plate extending substantially perpendicular to the axis of the brake drum, a pair of opposed brake shoes disposed adjacent one face of the back plate, one end of each shoe having engagement with an abutment surface fast to the back plate, and, a brake return spring acting on the two .shoes to urge'them towards each other, wherein the end of the spring is coupled to the respective shoes each by means of a coupling member which coacts with the back plate and the respective brake shoe to urge the brake shoe towards the said face of the back plate.

It is known to use a generally C-shaped spring to provide the required shoe return forces, particularly where limited space restricts the use of the more conventional helical coil springs, and it is possible and preferable to use sucha C-shaped spring in constructions in accordance with the present'invention, the two ends of the spring being coupled to the respective shoes in a manner which produces the required holddown forces.

A particular form of brake in accordance with the invention is, by way of example only, shown in the accompanying drawings and described below.

In the drawings:

FIG. 1 is a side elevation of the brake;

FIG. 2 is a section on the line B B of FIG. 1;

FIG. 3 is a section on the lineA A of FIG. 1; and

FIGS. 4 and 5 are a scrap section and perspective view, respectively illustrating constructional details. I

The brake shown in the drawings comprises a back plate 1 carrying a double ended hydraulic actuator or slave cylinder-2 and a double-ended abutment 3.'A pair of shoes 4T and 4L each have their opposite endsor tips engagingthe actuator and abutment respectively, and are urged inwardly (towards each other) by a generally C-shaped cantilever spring 6.

The end portion of each arm of the spring 6 is coupled to the adjacent shoe by means of a clip 7, the form of which is best seen in FIGS. 2, 4 arid 5 One end of the coupling member or clip extends through an opening 8 through the web 9 of the shoeand is-forrned with an-open loop which engages around the spring. Adjacent the loop, the portion 11 of the clip which extends through the opening 8 is inclined to the plane of the web. The other end portion of the clip is formed with a heel. portion l2 engagingone edge of an aperture 13 in the back plate, and a toe portion 14 engaging under the back plate, thus anchoring the coupling member to the back plate. The force exerted on a clip by the spring 6 'is parallel with the back plate, as indicated by arrow War in FIG. 4, and this produces a reaction R perpendicular to portion 11, and having components WRand Wl-I at right angles toeachother, and reactions WRI andWI-I are produced atthe points of engagementwith the backplate l. The forces acting in directions parallel with WI-I' serve to hold the shoe down against the back plate, while the;

shoe return loadis equal to WR. Clearly, the shoe return and holddown forces obtained can be determined by selection of the force Ws and the shaping of the clip -7, particularly the inclined portion 11 thereof. It will be noted that the heel and toe of the clip tend to be self sealinga'gainst the adjacent edges shoe-web window having a wear resistant slipper plate-26. The- I spindle 22 also extends through an eye at oneend of a strut 27:

comprising a tubular body portion 28, a nut 29 formed on its outer periphery with ratchet teeth, and a screw threaded spindle 31' in threaded engagement with the nut 29. The outer end of the spindle 31 is forked and engages in a notch in the adjacent shoe web. The lower end of the spindle 22 is supported in a spring clipv 32 which permits articulating movement of the spindle, and also spring biases the upper end of the spindle towards the back plate 1. The spring clip 32 extends longitudinally of the spindle and engages the upper end thereof, to provide the last-mentioned spring bias. The upper end of the spring clip 32 also provides axial location for a roller 24, which rotates on the spindle and engages the back plate to facilitate rocking movement of the spindle about its lower end, in a plane substantially parallel with that of the back plate.

For brake actuation through the above-described mechanism, the lever 21 is rotated (by means of a handbrake or other mechanical auxiliary mechanism) in a clockwise direction (as seen in FIG. 2) with the spindle 22. The finger 23 presses the shoe 4T to the right, and the reaction is transferred by the spindle 22 to the strut 27 and so to the shoe 4L, to expand the shoes against the action of the return spring 6.

The brake is provided with an automatic adjustment device for compensating for wear of the shoe friction linings. This device includes the strut 27 previously described, and operates to increase the effective length of the strut when wear compensating adjustment is required, by rotating the nut 29 in response to excess movement of the shoes upon brake actuation. This is effected by means of a pawl 30 forming one arm of a bellcrank lever, pivotally mounted on the spindle 22. The other arm-34 of the bell crank is secured to a cantilever spring 33, the free end of which bears against the web of the shoe 4L and also against the adjacent portion of the spindle 31. On assembly the spring is strained was to apply to the bell crank a force tending to rotate it clockwise as viewed in FIG. 2 and also to urge the free end of the pawl arm into engagement with the ratchet teeth formed on the nut 29.

In the brakes-off condition, the strut 27 is loaded by the return spring 6, and the resultant friction between the relatively-rotatable parts of the strut is sufficient to prevent the nut 28- rotating under the action of cantilever spring 33. On mechani cal actuation, the strut remains loaded, but when the service brake is actuated, the slave cylinder 2 expands the shoes, relieving the strut of load, so that if adjustment is required, the pawl can pick up'another ratchet tooth and rotatethe nut 28', and in this way, progressive wear of the friction linings is compensated as required, byrepeated operation. of the service brake, and the lost motion in the auxiliary brake, resulting from lining wear, is kept within acceptable, predetermined". limits. Adjustment'of the strut length byQthe pawl'and ratchet mechanism may, of course, be effected during-the actuating] stroke of the brake mechanism or the i return stroke.

Overstroking of .the pawl-is prevented byinterengagementzoft" small cooperating projections on the-pawl'bell'crankandrthe eye portion of the tubular member 28, respectively.

I claim:

1. In anintemal shoe drumbrakecomprising: aback. plate;- having a face extending substantially perpendicular; totheaxis. of the brake drum; a pair of brake shoesdisposedadjaoentr said face .of the back plate; abutmentsurfaces fast-tosaidbaclt: plate with which one end of each of said brakeshoeszisinvenzgagement; brake-actuating means-operable to forceapamtheother ends of said brake shoes; and a single Gshfimdfimntilfeverspring acting on said brake shoes to urgethem-together' (thereby holdingtheir first mentioned ends agairtst asaidjaltut,=- ment surfaces); the improvement which comprises: a pain-of coupling means connecting opposite. ends of said brake, spring to said shoes and-to said back plate, said coupling means being constructed and arranged to coactwithsaid shoes and -withsaid back plate to transmit'thereto a force frorn-said spring urging said shoes against said surfaceof said backplatta.

'2. The improved brake of claim 1,, wherein eachwsaid;

coupling meanscomprising acoupling member. having-;one:

.end portion coupled to said back plate, a second portion-- brake shoes has a web formed with an aperture, said coupling element extending through said aperture and said inclined portion engaging an edge of said aperture. 

1. In an internal shoe drum brake comprising: a back plate having a face extending substantially perpendicular to the axis of the brake drum; a pair of brake shoes disposed adjacent said face of the back plate; abutment surfaces fast to said back plate with which one end of each of said brake shoes is in engagement; brake-actuating means operable to force apart the other ends of said brake shoes; and a single C-shaped cantilever spring acting on said brake shoes to urge them together (thereby holding their first mentioned ends against said abutment surfaces); the improvement which comprises: a pair of coupling means connecting opposite ends of said brake spring to said shoes and to said back plate, said coupling means being constructed and arranged to coact with said shoes and with said back plate to transmit thereto a force from said spring urging said shoes against said surface of said back plate.
 2. The improved brake of claim 1, wherein each said coupling means comprising a coupling member having one end portion coupled to said back plate, a second portion inclined to the plane of said back plate and having sliding engagement with one said brake shoe, and a further portion coupled to one end of said spring.
 3. The improved brake of claim 2, wherein each of said brake shoes has a web formed with an aperture, said coupling element extending through said aperture and said inclined portion engaging an edge of said aperture. 